Field of the Invention
The present disclosure relates to control for an image forming apparatus, and particularly to control for a fixing device included in an electrophotographic image forming apparatus.
Description of the Related Art
An electrophotographic image forming apparatus becomes widespread. The electrophotographic image forming apparatus performs, as a printing process, a step of forming a toner image on a photosensitive body according to an input image, a step of primarily transferring the toner image on the photosensitive body to a transfer belt, a step of secondarily transferring the toner image on the transfer belt to a sheet, and a step of fixing the toner image to the sheet by heat using a fixing device.
The fixing device includes a fixing roller and a pressurizing roller. The fixing roller includes a heater. The heater heats the fixing roller. The pressurizing roller brings the sheet, which passes between the pressurizing roller and the fixing roller, into pressure contact with the fixing roller. Therefore, the sheet is pressurized and heated to fix the toner image onto the sheet.
In order to fix the toner image to the sheet, it is necessary for the fixing device to heat the sheet to a predetermined temperature or higher. For the purpose of energy saving, it is desirable to reduce energy necessary to heat the fixing device. As a technique for energy saving, for example, Japanese Laid-Open Patent Publication No. 2011-123479 discloses a fixing device in which, while the energy saving is achieved, a temperature drop of a heating roller due to paper feeding can be reduced and a neighborhood of a nip portion of the heating roller can rapidly be heated to a fixable temperature.
In the fixing device of Japanese Laid-Open Patent Publication No. 2011-123479, a heat storage material that changes between a liquid phase and a solid phase is used to achieve the energy saving. The heat storage material changes from the solid phase to the liquid phase after the printing, thereby absorbing heat. When a shock is given to the heat storage material at the beginning of the printing, the heat storage material changes from the liquid phase to the solid phase, whereby the heat storage material radiates the heat by the phase change. In the fixing device, the energy necessary to heat the fixing device is reduced using the heat radiation of the heat storage material. However, when a material that changes to the liquid phase is used as the heat storage material, a configuration preventing liquid leakage is required, which complicates a configuration of the fixing device.